压力诱导相变原位构建BiVO4/Bi0.6Y0.4VO4型异质结增强光催化全解水性能

光催化完全分解水制氢是一个在粉末颗粒中实现多个串行物理化学步骤的复杂反应过程.这一过程在理论上具有体系简单、成本低、易操作等特点.然而,单步光激发系统中通常存在严重的光生载流子复合,这极大地制约了光催化的整体效率.利用能带结构不同的半导体合理构建异质结催化剂被认为是解决这一难题的重要途径之一.特别是近年来,S型异质结概念的提出为设计异质结结构以及分析不同半导体之间的载流子迁移问题提供了新的思路.本文以小粒径BiVO₄/Bi_0.6Y_0.4VO₄(BYV)为研究对象,首先利用"共沉淀-晶化"的方法制备了BYV固溶体纳米颗粒,随后利用压力诱导固溶体中四方相钒酸铋结构转变为单斜相,从而构建了BiVO₄/Bi_0.6Y_0.4VO₄复合光催化剂.XRD,Raman,HRTEM,HAADF-EDS的结果表明,经过高压后处理的BYV固溶体表面会出现粒径约为5 nm单斜钒酸铋纳米颗粒,实现了原位构建异质结结构.随后载流子动力学的相关表征以及Au选择性光沉积的结果表明,在光照条件下,所构建异质结中的光生电子主要分布在BYV固溶体上,而在表面形成的单斜相钒酸铋颗粒主要起到了类似"空穴"捕获的作用.这种在异质结中的载流子迁移路径符合S型异质结机理.电化学、稳态荧光光谱以及瞬态荧光光谱的表征结果表明,相比于单一固溶体,在S型异质结这种两步激发系统中所存在的载流子迁移路径能够大幅促进光生载流子分离,从而提高了小粒径BYV的光催化完全分解水性能.综上,构建S型异质结是一种解决小粒径光催化剂中载流子分离能力差的有效途径.同时,压力诱导材料晶型转变实现原位构建异质结的制备方法也为提高光生载流子分离效率提供了新的研究思路与机遇.

In-situ pressure-induced BiVO4/Bi0.6Y0.4VO4 S-scheme heterojunction for enhanced photocatalytic overall water splitting activity

Step-scheme (S-scheme) heterojunctions in photocatalysts can provide novel and practical insight on promoting photogenerated carrier separation. The latter is critical in controlling the overall efficiency in one-step photoexcitation systems. In this study, a nanosized Bi0.6Y0.4VO4 solid solution was prepared by a coprecipitation method following with hydrothermal or calcination processes. The S-scheme heterojunction was fabricated by in-situ pressure-induced transformations of bis-muth vanadate from the tetragonal zircon phase to the monoclinic scheelite phase, which led to the formation of BiVO4 nanoparticles with a diameter of approximately 5 nm on the surface of Bi0.6Y0.4VO4. Bi0.6Y0.4VO4 with S-scheme heterojunctions showed significantly enhanced photocatalyt-ic overall water splitting activity compared with using bare Bi0.6Y0.4VO4. Characterization of the carrier dynamics demonstrated that a superior carrier separation through S-type heterojunctions might have caused the enhanced overall water splitting (OWS) activity. Surface photovoltage spec-tra and the results of selective photodeposition experiments indicated that the photogenerated holes mainly migrated to the BiVO4 nanoparticles in the heterojunction. This confirmed that the charge transfer route corresponds to an S-scheme rather than a type-Ⅱ heterojunction mechanism under light illumination. This study presents a facile and efficient strategy to construct S-scheme heterojunctions through a pressure-induced phase transition. The results demonstrated that S-scheme junctions composed of different crystalline phases can boost the carrier separation capac-ity and eventually improve the photocatalytic OWS activity.